Winter indoor sowing: what to sow from November to February (and how)

Winter doesn't stop sowing — it moves it. Indoors, November to February is the most productive stretch of the year for anyone wanting tomato, pepper or lettuce seedlings ready by spring. Here is the month-by-month calendar and the three settings that make the difference.

The calendar: what to sow when

• November-December: winter lettuce can still be sown, starting it indoors; in a cold greenhouse, seeds germinate above 5 °C.
• Mid-January: the first sowings can be launched — lettuces first, pricked out later.
• Late January: into modular trays — onions (4 seeds per cell), leeks, coriander. And the Mediterranean exception: aubergine, the one tender plant you can sow in January.
• Mid-February: sow peppers in a flat tray — and February is also time to sow all the warmth-loving Mediterranean vegetables: tomatoes, chillies, basil. General rule: peppers and aubergines about 6 to 8 weeks before the last frost.
• Mid-March: prick out the pepper seedlings.

Light: the limiting factor

• 14 to 16 hours: after sprouting, seedlings need 14 to 16 hours of bright light — a winter day's light window (9 h) is not enough.
• Very close: the light source must stay very close to the seedlings — the lamp almost touching.
• Stretching = verdict: stems that elongate and stretch = not enough light, no question.
• In numbers: tomatoes need 18 to 30 mol/m²/d of daily light (DLI); the calculation: PPFD × hours × 0.0036 = DLI. A lamp at 200 µmol at 25 cm is the difference between a stocky seedling and a leggy one.

Heat and humidity

• 20 to 26 °C: many seeds germinate well in this range. The heating mat can speed up germination — it warms the medium 5 to 10 °C above ambient temperature.
• Golden rule: use a heat mat specifically designed for seed germination, not any old pad; a thermostat is optional for precise tracking.
• After emergence: remove the mat once the seedlings are up.
• Humidity dome: it raises humidity around the seeds at sowing, then comes off once all seedlings have germinated. Plus adequate air circulation to prevent damping-off.

The last trap: forgetting to harden off

A seedling raised at 22 °C won't survive a brutal move outdoors: harden off before transplanting when seedlings are 3-4 cm tall — a week of progressive acclimatisation. And for those who like the cold technique: some trees demand a spell in the fridge — see stratifying pits.

Where to start?

The trio covering all three settings: the complete germination kit (greenhouse + LED + heating mat), the LED lamp alone to top up a windowsill, and the heating mat to speed up capricious germination. Our seasonal guides: chilli, bell pepper, aubergine and basil — the four champions of winter sowing.